Guide to Significant Wildlife Habitat - Door County Web Map

GRAND TRAVERSE ISLANDS
LOCATION:
The Grand Traverse Islands (or Lake Michigan Islands) includes all of the major islands located
in the water surrounding Door County, such as Pilot Island (T32N, R30E), Plum Island (T33N, R30E),
Washington Island (T33-34N, R30E), Detroit Island (T32-33N, R30E), Rock Island (T34N, R30E), and
Chambers Island (T31N, R29E). Smaller islands included in this landscape are Cana Island (T30N,
R29E), Horseshoe Island (T31N, R26E), Hat Island (T30N, R26E), Adventure/Strawberry Island (T31N,
R 26E), Little Strawberry Island (T31N, R26E), Jack Island (T31N, R26E), Sister Islands (T31N, R27E),
Spider Island (T31N, R29E), Gravel Island (T32N, R29E), Hog Island (T33N, R30E), and Fish Island
(T33N, R30E). As this report represents general areas of concern, exact locations of boundary lines have
not been designated.
GENERAL SITE DESCRIPTION:
Surrounding the Door Peninsula is a chain of islands in Lake Michigan and Green Bay called the
Grand Traverse Islands. Grand Traverse refers to the route travelers followed; once they came to Rock
Island, a “Grand Traverse” was made across Lake Michigan to the southern peninsula (Holand 1917).
Most islands (except Chambers Island) are underlain by Silurian dolostone with outcrops along
shorelines and an occasional interior escarpment. Dolostone shoreline communities known as Great
Lakes alkaline rock shores are present on eastern and southeastern coasts of the islands. Sometimes these
communities grade into alvar, a globally rare plant assemblage. Of the 19 islands in the Grand Traverse,
17 are located in Door County and are discussed. Pilot, Plum, Washington, Detroit, Rock, and Chambers
Islands have been studied at length and descriptions are fairly detailed. These islands are also labeled
accordingly on site maps.
Cana Island and Horseshoe Island are both small and have been less well documented. The other
islands are considered smaller ‘bird’ islands. They include Hat Island, Adventure Island, Little
Strawberry Island, Jack Island, Sister Island, Spider Island, Gravel Island, Hog Island, and Fish Island.
The bird islands are now predominantly used by colonial waterbirds such as Herring Gulls (Larus
argentatus) and Double-crested Cormorants (Phalacrocorax auritus). Their value for rare plant and
animal communities has thus been degraded (Judziewicz and Kopitzke 1999).
ECOLOGICAL SIGNIFICANCE:
Five State Natural Areas have been designated at various sites among the Grand Traverse Islands:
Jackson Harbor Ridges, Big & Little Marsh, and Coffee Swamp all on Washington Island. Rock Island is
a state park and a large portion of the island, Rock Island Woods, is a State Natural Area. Sister Islands is
also State Natural Area. Washington Island has several exposed areas of escarpment along the northern,
western, and southeastern edges with 20-120 foot tall bluffs. All of these islands form a portion of the
Niagara Escarpment. Nearly 850 acres of wetlands (Coffee Swamp, Jackson Harbor Ridges, Big and
Little Marsh, and Boyer’s Bluff) are found near the eastern and northwestern portions of Washington
Island.
. When comparing the islands with data from 25-75 years ago drastic changes can be seen
(Judziewicz and Kopitzke 1999). Vegetation on the smaller islands has been severely impacted by
colonial water birds in the last decade. Human residential developments and white-tailed deer herbivory
are widespread on most islands. The sensitive nature of the plant and animal assemblage makes them
particularly susceptible to human disturbance. Despite Door Peninsula’s islands having been severely
impacted by human activity in the late 19 th and early 20 th century, evidence is clear that the many of these
islands still house some of the richest rare plant reserves in Wisconsin.
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